In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure of radial rays such as light or electron beam through a mask having a predetermined pattern, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film. A resist material in which the exposed portions become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions become insoluble in a developing solution is called a negative-type.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are starting to be introduced in mass production. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a wavelength shorter than these excimer lasers, such as F2 excimer lasers, electron beam, extreme ultraviolet radiation (EUV), and X-ray.
Resist materials for use with these types of exposure light sources require lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources. As a resist material which satisfies these conditions, a chemically amplified resist is used, which is obtained by dissolving a base resin that exhibits a changed solubility in an alkali developing solution under action of acid and an acid generator that generates acid upon exposure in an organic solvent. For example, a chemically amplified positive resist is obtained by dissolving, as a base resin, a resin which exhibits increased solubility in an alkali developing solution under action of acid, and an acid generator, in an organic solvent. In the formation of a resist pattern, when acid is generated from the acid generator upon exposure, the exposed portions become soluble in an alkali developing solution.
Until recently, polyhydroxystyrene (PHS) or derivative resins thereof in which the hydroxyl groups are protected with acid-dissociable, dissolution-inhibiting groups (PHS-based resins), which exhibit high transparency to a KrF excimer laser (248 nm), have been used as the base resin component of chemically amplified resists. However, because PHS-based resins contain aromatic rings such as benzene rings, their transparency is inadequate for light with wavelengths shorter than 248 nm, such as light of 193 nm. Accordingly, chemically amplified resists that use a PHS-based resin as the base resin component suffer from low levels of resolution in processes that use light of 193 nm.
Resins that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are now widely used as base resins for resists that use ArF excimer laser lithography, as they exhibit excellent transparency in the vicinity of 193 nm (for example, see Patent Document 1).
Further, resist compositions in which the aforementioned acrylic resins are dissolved in an organic solvent, such as propylene glycol monomethyl ether acetate (PGMEA), propylene glycol monomethyl ether (PGME), cyclohexanone, 2-heptanone and ethyl lactate (EL) are now widely used as resists that use ArF excimer laser lithography.
In the meantime, as the miniaturization of resist patterns has progressed in recent years, a double patterning process has been proposed, as one of the lithography techniques in order to further improve the resolution, in which a resist pattern is formed by conducting a patterning process twice or more (for example, refer to Non-Patent Documents 1 and 2).
According to the double patterning process, for example, a first resist pattern is formed on a substrate by forming a resist film using a first resist composition and patterning the resist film, followed by formation of a resist film using a second resist composition on the substrate on which the first resist pattern is formed, and patterning of the resist film. As a result, a resist pattern can be formed with a higher level of resolution than that of the resist pattern formed through one single patterning process.
In the double patterning process, the first resist pattern is likely to be adversely affected during the application of the second resist composition. That is, problems such as the following arise. For example, a portion of, or all of the first resist pattern is dissolved by the solvent for the second resist composition, thereby causing thickness loss or the like, which deteriorates the shape of the resist pattern. Moreover, so-called mixing occurs in which the first resist pattern and the second resist composition dissolve within each other, making it impossible to form a resist pattern with an excellent shape.
It is thought that such problems can be solved by using a resist composition that uses an organic solvent in which the first resist pattern hardly dissolves, as the second resist composition. Accordingly, when using a positive resist composition as the first resist composition, a negative resist composition hitherto has been widely used as the second resist composition which has a low compatibility with the positive resist composition and which also uses an organic solvent, such as an alcohol-based organic solvent, thus providing excellent solubility for the resist materials.